What this calculator does
A solar array generates one kind of kilowatt hour and it is worth two different amounts. Used in the house it saves you the import price. Sent to the grid it earns the feed-in tariff, which in most markets is now a fraction of that. The gap between the two is often five or six to one.
That makes self-consumption, the share of generation you use rather than export, the single most important number about a solar system after its size. The same array can be worth $1,100 a year or $1,900 a year depending on nothing but when the house uses power.
The formula
Split generation into the part used on site and the part exported. The self-consumed share is valued at the import price, because every unit avoids a purchase. The exported share earns the feed-in tariff. Add them for the yearly value. Self-consumption cannot exceed what the house actually uses, so asking for a share above that is capped and the calculator says so.
| Term | Meaning |
|---|---|
| Self-consumption | The share of generation used in the house at the moment it is produced. |
| Export | Generation sent to the grid, paid at the feed-in tariff. |
| Import price | What you pay per kilowatt hour. This is what each self-consumed unit saves you. |
| Feed-in tariff | What the retailer pays for exports. Rarely more than a third of the import price now. |
The inputs explained
| Field | What to enter |
|---|---|
| Generation per year (kWh) | Annual generation. The solar energy yield page estimates this from array size and sun hours. |
| Household use per year (kWh) | Total household consumption for the year, from your bills. |
| Share of generation used on site (%) | Share of generation used on site. Typically 20 to 40 per cent without a battery or load shifting, and higher if someone is home during the day. |
| Import price ($/kWh) | Import price per kilowatt hour, including anything that scales with usage. |
| Feed-in tariff ($/kWh) | Feed-in tariff per exported kilowatt hour. |
When to use it
Valuing an array you already own
Enter your real generation and the self-consumption share from your inverter app. The average value per kWh generated is the figure worth remembering, because it is usually far below the import price people assume they are saving.
Deciding whether load shifting is worth the bother
Running the dishwasher and washing machine at midday raises self-consumption. The last output shows what ten points is worth, which on these figures is $200 a year for no capital outlay at all.
Working out whether to add a battery
A battery raises self-consumption rather than generation. Find the self-consumption it would get you to, read the extra value, and compare that against the battery cost on the arbitrage page.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
What is self-consumption worth?
Only the share used on site changes.
| Self-consumption | Value of the array per year | Share actually achieved | Average value per kWh generated |
|---|---|---|---|
| 10% | $600.00 | 10.0% | $0.08 |
| 25% | $900.00 | 25.0% | $0.11 |
| 35% | $1,100.00 | 35.0% | $0.14 |
| 50% | $1,400.00 | 50.0% | $0.18 |
| 75% | $1,900.00 | 75.0% | $0.24 |
| 100% | $1,900.00 | 75.0% (capped by household use) | $0.24 |
How much does the feed-in tariff matter?
Only the export rate changes.
| Feed-in tariff | Value of the array per year | Average value per kWh generated |
|---|---|---|
| $0.00 | $840.00 | $0.11 |
| $0.03 | $996.00 | $0.12 |
| $0.05 | $1,100.00 | $0.14 |
| $0.10 | $1,360.00 | $0.17 |
| $0.20 | $1,880.00 | $0.24 |
| $0.30 | $2,400.00 | $0.30 |
Questions
Why is self-consumption worth so much more than export?
Because a self-consumed unit saves you the full retail import price, while an exported unit earns only the feed-in tariff. With a 30 cent import and a 5 cent tariff, using a kilowatt hour is worth six times exporting it.
What self-consumption should I expect?
Without a battery, typically 20 to 40 per cent for a household that is out during the day, and higher if someone is home or if large loads run at midday. Check your inverter app rather than guessing.
Why does the value stop rising above a certain share?
Because you cannot use more than you consume. Once the self-consumed figure reaches total household use, further generation can only be exported, and the calculator reports the capped share.
Does a battery increase generation?
No. It increases self-consumption by storing midday surplus for the evening. The array generates exactly the same amount either way.
Should I include the daily supply charge?
No. Solar does not avoid a fixed daily charge, only the per-kilowatt-hour part, so including it would overstate the saving.
For generation itself see solar energy yield and solar system sizing. For whether a battery earns its keep there is home battery arbitrage, and solar payback period turns a yearly saving into years.